Foley et al. disclose the results of their evaluation of the sliding frictional characteristics of cobalt on cobalt, nickel on nickel and iron on iron under different atmospheric conditions over a range of temperatures using a hemispherically shaped pin in continuous sliding contact at 3.63 m./min. on a rotating disk (R. T. Foley, M. B. Peterson, and C. Zapf, Frictional Characteristics of Cobalt, Nickel, and Iron as Influenced by Their Surface Oxide Films, ASLE Transactions 6, 1963, pp. 29-39). Although considerable data is presented that indicates that behavior varies widely among these different metals as the temperature and the atmosphere change, no guidance is given as to the potential behavior of complex systems such as alloyed steels.
Rabinowicz suggests that an oxide film of about 0.01 micron thickness on the base metal is needed to provide effective dry lubrication (E. Rabinowicz, Lubrication of Metal Surfaces by Oxide Films, ASLE Transactions 10, 1967, pp. 400-407). Considerable data is presented that indicates that behavior varies widely among different metals including nickel riding on type 303 stainless steel, type 303 stainless steel riding on nickel, nickel riding on nickel, and type 303 stainless steel riding on itself, as the temperature and the atmosphere change.
The surface treatment of metals to prevent corrosion is described in U.S. Pat. No. 4,017,336 to Foroulis. Foroulis describes pretreating the metals in the presence of oxidizers such as air at temperatures in the range of about 537.8-648.9° C. (1000-1200° F.) to form an oxygen barrier to sulfur attack.
A method of forming coatings of co-deposited aluminum oxide and titanium oxide on wear surfaces of substrates such as hardened or treated steel, or cemented carbides is disclosed in U.S. Pat. No. 4,052,530 to Fonzi. According to this patent the coating is formed by simultaneously reacting an aluminum halide gas and a titanium halide gas with water on a surface maintained at a temperature of about 482.2° C. (900° F.) to about 676.7° C. (1250° F.) The coating comprises alpha alumina (Al2O3) with about 2% to about 10% hexagonal alpha titanium oxide (Ti2O3) dispersed in the alumina matrix. The Fonzi process requires use of chemical vapor deposition with attendant special process equipment and costs, and may deleteriously affect the morphology of the substrate ferrous alloy due to use of relatively long times at temperatures.
U.S. Pat. No. 6,635,355 to Bianco et al. discloses a ferrous metal article having an adherent wear resistant coating of metallic oxides and a method of forming such a coating on an iron-chrome article. The oxides identified in this patent consist of hematite, magnetite and eskolaite.
This invention relates to chromium-nickel stainless steel alloy articles having a wear resistant coating of metallic oxides that are formed by frictional interaction of the iron oxide, chromium, nickel and copper layer resulting from the controlled oxidation of the base alloy. It is believed that these oxides will also form without any frictional interaction if the heat treated base alloy is subjected to temperatures greater than 815.6° C. (1500° F.) for a sufficient time in an oxidizing atmosphere. This coating of iron oxides, chromium, nickel and copper preferably comprise a coating on chromium-nickel stainless steel alloys of the following general composition expressed in weight percent: C 0.00-0.07, CR 11.0 - 18.0, Ni 3-9.5, Cu 1.5-5.0 with other minor alloying elements possibly present. Other alloying elements may be present. The coating has a thickness of from about 2.5 microns (0.1 mil) to about 203 microns (8 mils), and is formed by exposure of the article to an oxidizinq atmosphere, preferably air, preferably during heat treatment of the article.
The present invention also relates to friction braking systems and more particularly to aircraft friction disks with reinforced peripheral slots for use in multiple disk brakes. In brake assemblies which employ a plurality of brake disks alternately splined to the wheel and axle of an aircraft, it is important to provide specially constructed drive means to reinforce peripheral slots in the disks to relieve the severe stressing that otherwise would rapidly deteriorate the periphery of the disks. When disk brakes were constructed of steel, the disks were able to withstand the shearing and compressive forces exerted thereon between the slots and the torque transmitting members because of their physical properties. With the replacement of the steel disks with carbon and/or ceramic composite disks it is important to provide reinforcing drive inserts at the peripheral slots since the composite materials have less durability under this type of loading than steel. The drive inserts transmit the forces to the composite disks, over a larger area reducing the contact stresses which increases the load capability of the composite disks.
The present invention preferably utilizes a torque drive insert such as that described in U.S. Pat. No. 4,469,204. Such drive insert in the peripheral slots engages the composite disk and drives on the rotating member or transfers the stress to the stationary member without deleterious effects on the carbon composite materials. The drive insert has a pair of opposed faces which contact the opposite walls of the slots to distribute the load. The drive insert design uses a channel to retain the drive inserts in position within the slot. Such structure eliminates peeling or fraying of the carbon composite heat sink material while also taking up some of the stresses due to misalignment in the wheel and brake. The structure of the drive insert and clip provides for a large bearing area in the carbon composite and minimizes the weight required to obtain the strength to handle the side loads in case of some misalignment. The construction permits the drive insert to float freely in the slot of the carbon disk thereby eliminating the tension loading of the attaching rivets.